In a common application, an alternator is a rotating electrical machine that converts mechanical energy from an operating vehicle engine into electrical energy, which is used to supply power to electrical loads of the vehicle. For example, the electrical energy produced by the alternator charges a vehicle battery and supplies power to a headlight system. The alternator generally includes a rotatable electromagnet with field coil and a stator having a plurality of stator windings. Typically delivered through a belt drive system, operation of the engine supplies the alternator with mechanical energy, which results in rotation of the electromagnet relative to the stator windings. The rotating electromagnet's field coil is supplied with an electrical current, such that the field coil generates a rotating magnetic field. The rotating magnetic field induces an alternating current (“AC”) electrical energy in the stator windings. The alternator includes a rectifier to convert the AC electrical energy to a direct current (“DC”) output power. A vehicle wiring system couples the DC output power to the battery and the other electrical loads of the vehicle.
The alternator further includes a voltage regulator, which regulates and controls the DC output power according to its voltage by controlling the magnitude of the current supplied to the field coil. In particular, the voltage regulator maintains the DC output voltage at a particular set point voltage level, which depends primarily on the basic electrical design of the vehicle and its battery. The voltage regulator increases the magnitude of the field current in response to an increased electrical power demand from the vehicle, and the voltage regulator decreases the magnitude of the field current in response to a decreased electrical power demand from the alternator.
The amount of mechanical energy required to rotate the electromagnet relative to the stator depends on the magnitude of the power output of the alternator. When the voltage regulator increases the magnitude of the field current and thus electrical power output of the alternator in response to increase vehicle electrical load, a corresponding increase in the amount of mechanical energy (supplied by the vehicle engine) is required to rotate the field coil and induce the output. Conversely, when the voltage regulator decreases the magnitude of the field current, a decreased amount of mechanical energy is required to rotate the field coil.
The vehicle cranking battery is a chemical energy conversion device whose behavior is dependent upon temperature. When charging the battery in cold conditions, more voltage from the alternator is required in order to convert electrical charge into stored chemical potential energy. When charging the battery in hot conditions, a lower voltage is required to prevent damage to the battery as a result of excess electrical energy being converted to heat.
Typically, the modern voltage regulator is designed to adjust the vehicle voltage level according the temperature conditions of the vehicle.
The voltage regulator of a conventional alternator regulates the magnitude of the set point voltage level independent of the mechanical load on the vehicle engine. The mechanical load of the engine depends on, among other factors, the terrain upon which the vehicle is traveling and the driving style of the operator. For example, the mechanical load on the engine is generally at a minimum when the engine operates near idle speed, such as when an operator maintains the vehicle in a stationary position and when the operator activates the braking system to reduce the speed of the vehicle. In comparison, however, the mechanical load on the engine is generally at a maximum when the operator accelerates the vehicle, such as when accelerating to highway speed, for example. If an electrical component of the vehicle requires an increased level of electrical power at the same time the vehicle is accelerating, then the voltage regulator maintains the vehicle voltage level by increasing the electrical output. However, increasing the electrical output level increases the amount of mechanical energy required to rotate the field coil relative to the stator. This additional mechanical load imparted on the engine by the alternator may reduce the rate of acceleration of the vehicle. In response to the reduced acceleration, the vehicle operator may supply the engine with additional fuel, thereby reducing the fuel economy of the engine. Therefore, further advancements for vehicle alternators are desirable.